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Basics - Poster 1
Radioactive Emissions The first three to be discovered were Alpha ( α ), Beta ( β ) and Gamma ( γ )
The Atom
Alpha decay
A
A-4 X Y +
Z Z-2
4
He
2
Atomic Number ( Z )
This is the number of protons ( and determines what element it is )
Mass Number ( A ) This is the number of protons + number of neutrons
Number of electrons = number of protons An element X is written
A Z
X
An element , for example , potassium , can have more than one isotope . For each isotope , the atomic number ( Z ) will be the same , but the mass number ( A ) will be different , depending on
Alpha particles are very much bigger than electrons . They are made up of two protons and two neutrons bound together , the same as a helium nucleus .
In both alpha and beta decay the remaining atom is a different element . how many neutrons are included in the atom . Some isotopes may be radioactive and emit radiation such as alpha , beta or gamma , while others will be stable and emit no radiation . For example , the naturally occurring potassium isotope K ( also
19 written as K-40 or potassium-40 ) is radioactive , but the most
40
Gamma decay
39 abundant potassium isotope K ( or K-39 ) is stable .
19
Beta decay
A
A
X Y +
Z Z + 1 β
0 -1 e
A
X *
Z
After an alpha or beta decay , the nucleus is often in an excited state and releases energy in the form of a gamma photon .
In beta decay of an unstable nucleus a neutron splits into a proton and an electron .
The electron is ejected from the nucleus at high speed and the maximum energy of the electron is characteristic of the nuclide .
The atom remains the same element .
Some examples are amercium-241 ( Am-241 ) which emits alpha and gamma , and cobalt-60 ( Co-60 ) which emits beta and gamma .
Images provided by courtesy of Public Health England